For years doctors and skin cancer experts have been telling the public to apply sunscreen on a daily basis to protect against harmful exposure to ultraviolet rays.

The Skin Cancer Foundation offers that skin cancer is the most common form of cancer in the United States. More than 3.5 million skin cancers in more than two million people are diagnosed annually. Health Canada states that skin cancer accounts for one-third of all new cases of cancer in Canada.

But are the products we slather on our skin to protect against skin cancer doing any harm?

As it turns out, most sunscreens themselves are not necessarily harmful. But the false sense of security sunscreens provide that might be harmful, especially ones with higher levels of SPF.

Many of the "sport" or "active" products on the market boast a high level of SPF and waterproof capabilities. Individuals who apply these products may think it's a one-time deal and they're adequately protected. However, even an SPF 50 product is only as effective as the manner in which it was applied and how frequently. Too often people do not apply enough product and not nearly as frequently as they should, and burns and skin damage often result.

Although sunscreens are a good idea, some manufacturers add ingredients that may actually damage the skin cells the products are meant to protect. According to a 2010 report from the Environmental Working Group, only 39 of the 500 products they examined were considered safe and effective to use.

Some manufacturers inflate SPF inaccurately, causing consumers to believe they're getting more protection than they really are. Others are adding vitamin A and its derivatives, retinol and retinyl palmitate to formulations.

Their reasoning is that vitamin A is an antioxidant that slows skin aging. However the EWG has examined safetyreports that indicate vitamin A may contribute to cancerous tumors when used on skin exposed to sunlight.

Other products outside of sunscreens that contain vitamin A even warn consumers that retinol and vitamin A can increase the skin's sensitivity to sunlight and that prolonged exposure should be avoided.

In most cases, an effective sunscreen prevents more damage than it causes, but consumers should have accurate information on sunscreen limitations and on the potentially harmful chemicals in some of those products.

There is also the matter of wearing sunscreen the right way. When going out in the sun:

Apply sunscreen at least 30 minutes beforehand.

Use a teaspoon on your face and a shot-glass amount on the body to achieve the SPF listed on the package.

Don't forget to apply sunscreen to your ears, lips, forehead and the part in your hair. Bald individuals should also apply all over their heads.

Reapply every 2 hours or more frequently if you have been swimming or sweating heavily.

Use a hat and sun protective clothing as an added measure of protection.

Use new sunblock every year otherwise you risk an ineffective product.